The task to create networks in environments where many wireless networks are simultaneously operating has always been a challenge. Such environments are typically found in urban and industrial areas. Interference from other wireless devices will vary over time due to the fact that some wireless networks are used more at certain hours of the day, and others new wireless networks may also be installed. An example of this is WiFi usage in a residential area which is often used more heavily during the evenings and weekends.
The prior art technique for interference free coverage in wireless networks is to only allow signals within a frequency interval for a specific wireless network, which often requires a governmental license, as illustrated in FIG. 1. Examples of such networks are GSM and television broadcasting, see for instance EN 301 511, Global System for Mobile communications (GSM).
If a network is expanded to cover a large area where a number of WiFi networks and other wireless networks are operating, the problem with interference arises. The use of the same communication parameters, such as frequency, in the different networks may result in disrupted communication. Although the WiFi hotspots are out of range of each other, they are within the coverage area of the expanded large area network. It should be noted that not only the expanded large area network may be disrupted due to the interference between the networks, but most certainly the local WiFi networks will be disrupted resulting in a lower quality of service for the WiFi hotspots.
A typical example is a multi-storey office building having a WiFi network on each and every floor. Sometimes many local WiFi areas may be found on the same floor. The sum of all frequencies used within the entire building, which may be considered to be a large area network, results in a loss of available frequencies to use. This may result in communication drop outs. In addition to this, other wireless more mobile devices, such as wireless headsets, may be frequently used within the multi-storey building further increasing the density temporarily. Wireless headsets generally operate using Bluetooth 2.0, using an adaptive frequency selection algorithm that only tries to find a method to optimize its own data throughput sometimes at a cost of other networks throughput.
Thus, a general drawback with prior art wireless networks is that the risk for interference between different wireless networks increases when they operate within the same coverage area using frequencies close to each other. This drawback applies to any network using a shared medium, such as a fiber network.
A solution has been presented in WO 2007/009043, reference [1] describing a method to selecting communication channels in order to reduce the interference in a communication system, by adaptive frequency hopping or background monitoring to identify incumbent users.
Another solution has been presented in an article with the title “Interference Mitigation Using Spectrum Sensing”, reference [2] describing a method to reduce interference by spectrum detection, by detecting interfering networks and adapting communication parameters in response thereto.
A drawback with the solutions to reduce the interference when communicating in a communication network is that the information communicated during a time slot uses a dedicated frequency channel and in order to prevent interference, the used frequency channel needs to be free from interferences of other networks. This will reduce the number of available frequency channels that could be used for communication.